Re: [ozmidwifery] Vaginal ultrasounds

[Marilyn Kleidon]

Just goes to show how quickly the research changes. I just graduated and we were taught never to rely on any u/s other than a first trimester u/s for dating (and that only if the mom had no idea of dates as referred to previously). The research just 6 months ago was saying +/- 2weeks at 18 - 20 weeks and +/- 1 week at 11-13 weeks. This was not because of the accuracy of the u/s but the then understood "fact" that in the first trimester there is little individual variation in size for most gestations that is most 8 weeks pregnancies will have the same size sac, embryo etc. and so individual variation will have little or a small effect if any on size. So a relialable estimation of dates can be made based on size. However, from the first trimester individual variation takes over and not all 20 week fetuses will be the same size and so while the u/s sound measurement may be accurate to 1 week or even +/- 3 days, the variation in size due to genetics must also be taken into account. Please correct me if there is research to indicate that individual growth variations occur later in pregnancy than the 2nd trimester. This is why we were taught not to rely on later u/s (post 1st trimester) for dates if u/s was the dating method. Obviously this is a field that is changing very quickly. I agree that abdominal u/s for nuchal fold thickness should be the method of choice and vaginal u/s only used if resolution cannot be obtained, a decision the sonographer is qualified to make. Again continuity of care and  time in prenatals to discuss options with women is vital, reliance on technology really brings the issue of informed choice into focus. marilyn ----- Original Message ----- From: Debby M To: [EMAIL PROTECTED] Sent: Sunday, September 08, 2002 2:27 PM Subject: Re: [ozmidwifery] Vaginal ultrasounds Hi Marilyn and everyone, Ref the dating.  I checked with my other half who is a sonographer and he agreed that US up to 20wks is accurate for dating.  He indicated that US at 20wks was usually +/- 3 days, earlier than this it was +/- 5-7days and later than this could vary considerably - especially in 3rd trimester (hence the reason US is not a good predictor of fetal weight and birth size - another scare tactic often used to encourage early induction or csec).   The problem with anatomical ultrasound of the fetus much before 18wks is that fetal measurements are too small to diagnose some major deformities - particularly of the heart and other organs - hence the recommendation for the US at this stage.  However I personally would question how many women actually have terminations at this stage even if they are told bubs condition is fatal. You are quite right about nucal fold it is only relevant if done between 11 and 14 wks, but like all US is only an indicator of a risk not a definative diagnosis.  He also indicated that a competent sonographer can get an accurate nuchal fold measurement abdominally in over 90% of clients, it is rare for them to have to do vaginal US - does this raise doubts about the sonography competence of some of the OBs doing this procedure?  Maybe they should leave it to those who do years of training in it - the sonographers and radiologists - but then their own pockets wouldn't be lined (cynical I know). But of course all these "facts" still don't seem to justify the argument for routine early first trimester vaginal ultrasounds - so we really still don't have a justifiable answer - except the power thing. Debby Send and receive Hotmail on your mobile device: Click Here -- This mailing list is sponsored by ACE Graphics. Visit to subscribe or unsubscribe.